Annotation of sys/lib/libkern/arch/alpha/ffs.S, Revision 1.1
1.1 ! nbrk 1: /* $OpenBSD: ffs.S,v 1.1 1996/10/31 00:43:18 niklas Exp $ */
! 2: /* $NetBSD: ffs.S,v 1.3 1996/10/17 04:26:26 cgd Exp $ */
! 3:
! 4: /*
! 5: * Copyright (c) 1995 Christopher G. Demetriou
! 6: * All rights reserved.
! 7: *
! 8: * Redistribution and use in source and binary forms, with or without
! 9: * modification, are permitted provided that the following conditions
! 10: * are met:
! 11: * 1. Redistributions of source code must retain the above copyright
! 12: * notice, this list of conditions and the following disclaimer.
! 13: * 2. Redistributions in binary form must reproduce the above copyright
! 14: * notice, this list of conditions and the following disclaimer in the
! 15: * documentation and/or other materials provided with the distribution.
! 16: * 3. All advertising materials mentioning features or use of this software
! 17: * must display the following acknowledgement:
! 18: * This product includes software developed by Christopher G. Demetriou
! 19: * for the NetBSD Project.
! 20: * 4. The name of the author may not be used to endorse or promote products
! 21: * derived from this software without specific prior written permission
! 22: *
! 23: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
! 24: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
! 25: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
! 26: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
! 27: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
! 28: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
! 29: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
! 30: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
! 31: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
! 32: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
! 33: */
! 34:
! 35: #include <machine/asm.h>
! 36:
! 37: LEAF(ffs, 1)
! 38: addl a0, 0, t0
! 39: beq t0, Lallzero
! 40:
! 41: /*
! 42: * Initialize return value (v0), and set up t1 so that it
! 43: * contains the mask with only the lowest bit set.
! 44: */
! 45: subl zero, t0, t1
! 46: ldil v0, 1
! 47: and t0, t1, t1
! 48:
! 49: and t1, 0xff, t2
! 50: bne t2, Ldo8
! 51:
! 52: /*
! 53: * If lower 16 bits empty, add 16 to result and use upper 16.
! 54: */
! 55: zapnot t1, 0x03, t3
! 56: bne t3, Ldo16
! 57: sra t1, 16, t1
! 58: addl v0, 16, v0
! 59:
! 60: Ldo16:
! 61: /*
! 62: * If lower 8 bits empty, add 8 to result and use upper 8.
! 63: */
! 64: and t1, 0xff, t4
! 65: bne t4, Ldo8
! 66: sra t1, 8, t1
! 67: addl v0, 8, v0
! 68:
! 69: Ldo8:
! 70: and t1, 0x0f, t5 /* lower 4 of 8 empty? */
! 71: and t1, 0x33, t6 /* lower 2 of each 4 empty? */
! 72: and t1, 0x55, t7 /* lower 1 of each 2 empty? */
! 73:
! 74: /* If lower 4 bits empty, add 4 to result. */
! 75: bne t5, Ldo4
! 76: addl v0, 4, v0
! 77:
! 78: Ldo4: /* If lower 2 bits of each 4 empty, add 2 to result. */
! 79: bne t6, Ldo2
! 80: addl v0, 2, v0
! 81:
! 82: Ldo2: /* If lower bit of each 2 empty, add 1 to result. */
! 83: bne t7, Ldone
! 84: addl v0, 1, v0
! 85:
! 86: Ldone:
! 87: RET
! 88:
! 89: Lallzero:
! 90: bis zero, zero, v0
! 91: RET
! 92: END(ffs)
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